Production of organic amides from organic nitriles

ABSTRACT

ORGANIC AMIDES ARE PRODUCED FROM ORGANIC NITRILES BY AN ELECTROLYTIC METHOD. THE PROCESS IS ESPECIALLY APPLICABLE TO THE PREPARATION OF ACRYLAMIDE FROM ACRYLONITRILE.

United States Patent O'fliee 3,764,494 Patented Oct. 9, 1973 3,764,494 PRODUCTION OF ORGANIC AMlDES FROM ORGANIC NITRILES Ronald J. Allain and David G. Braithwaite, Brookhaven, Miss., assignors to Nalco Chemical Company, Chicago, Ill. No Drawing. Filed June 1, 1972, Ser. No. 258,866 Int. Cl. C07b 29/06; C07c 103/08, 103/12 US. Cl. 204-74 6 Claims ABSTRACT OF THE DISCLOSURE Organic amides are produced from organic nitriles by an electrolytic method. The process is especially applicable to the preparation of acrylamide from acrylonitrile.

BACKGROUND It is known in the art that organic nitriles in the presence of water and a copper catalyst can be converted to amides, acids and other hydrolyzed products. US. Pat. 3,381,034 and the publications cited therein, and US. Pat. 3,631,104 and the publications cited therein describe various processes of this type. The modus operandi of these processes is not clearly understood and the results obtained appear to be somewhat erratic.

Both of the aforementioned patents describe processes which are said to be applicable to the preparation of acrylamide from acrylonitrile. Acrylamide is a well known intermediate which is useful in forming homopolymers and also in forming copolymers with other olefinically unsaturated organic compounds. It would, therefore, be desirable to provide a new and improved process for the preparation of acrylamide from acrylonitrile which is also suitable for the preparation of other organic amides from organic nitriles.

OBJECTS One of the objects of the present invention is to provide a new and improved process for preparing organic amides from organic nitriles wherein an electrolytic method is used.

Another object of the invention is to provide a new and improved process for preparing acrylamide from acrylonitrile. Other objects will appear hereinafter.

BRIEF SUMMARY OF THE INVENTION In accordance with the invention an organic nitrile is converted to an organic amide by passing organic nitrile in the presence of water and under alkaline pH conditions through an electrolytic cell containing spaced electrodes at least one of which contains or is made from copper while subjecting it to a direct current from said electrodes.

DETAILED DESCRIPTION OF THE INVENTION For the purpose of the invention it is preferable to use a cell of the type disclosed in U.S. Pats. 3,141,841, 3,287,249, and 3,368,961. In this type of cell the electrolyte can be continually recirculated through the cell during a cell run. One of the electrodes, which is usually tubular and can be a pipe, serves as a container for the electrolyte and the other electrode usually consists of metal pellets separated from the first electrode by a foraminous insulating material so as to prevent short circuiting. In one type of system which can be employed in the present invention the electrolyte consisting of a solution of the organic nitrile is pumped into the top of the electrolytic cell and withdrawn through the bottom of the cell and then recirculated through a surge drum or tank back to the top of the cell. Systems of this type using a surge drum or tank are described in US. 3,567,600 and 3,572,932. The flow of the electrolyte can also be reversed so that it is introduced into the bottom of the cell and withdrawn from the top. This is a closed system and therefore usually operates under a superatmospheric pressure which is desirable because some nitriles such as acrylonitrile are gases at elevated tempera tures and also because the electrolytic action is carried out in the presence of water which vaporizes at elevated temperatures. Acrylonitrile is a gas at 70 C. and, of course, water boils at 100 C.

One way of practicing the invention is to use a cell of the type described in which one electrode is an outer tubular member and the other electrode consists of copper shot disposed within a foraminous bag made from a chemically inert material as described in the aforementioned cell patents and so arranged that the electrolyte is free to flow through the cell from top to bottom or vice versa. In this case, the outer electrode is preferably made from stainless steel or another metal which is not electrolyzed. The outer electrode can also be made from copper or a copper-containing metal which is not electrolyzed. Attempts have been made to use a cell constructed of mild steel and while it is possible to convert an organic nitrile to an organic amide using this type of cell, the order of conversion is relatively low due to the fact that the steel apparently is electrolyzed to form iron-containing compounds.

The voltages and amperages employed can be varied and the voltages and amperages required to produce optimum conversions can be obtained by routine experiments.

It is desirable to reverse the polarity of the electrodes periodically in order to prevent build up of electrically deposited copper on one electrode or the other.

In carrying out this process, the pH appears to be critical and should not be on the acid side. Usually the pH is within the range of 7 to 10.5. Higher pHs can be used but are likely to produce by-products such as cyanohydrin.

The temperatures used are subject to variation. Usually moderate temperatures of the order of -120 F. are employed but higher temperatures can be used. However, higher temperatures may require the use of higher pressures and also the use of more expensive equipment.

The pressures employed are normally moderate and usually within the range of 10-15 pounds per square inch gauge (p.s.i.g.) but higher pressures can be used.

The invention will be further illustrated but is not limited by the following examples in which the quantities are given in parts by weight unless otherwise indicated.

Example I A small 1 inch diameter pipe cell of the type previously described was constructed of stainless steel and was set up in a recirculation system containing a pump and a surge tank whereby an electrolyte could be pumped into the top of the cell and recirculated through the cell out the bottom into the surge tank and then back through the pump to the top of the cell. The cell was loaded with copper shot contained in a foraminous insulating container which separated the copper shot from the inside surface of the stainless steel pipe. Thus the stainless steel pipe formed one electrode and the copper shot another electrode. The cell was heated by means of heating tape and a direct current voltage of 10 volts at 5 amperes was applied across the electrodes. The polarity of the electrodes was reversed every 5 seconds. A temperature of 110-120 F. was maintained and the pressure in the closed system was 10-15 p.s.i.g.

In an initial experiment a 7% solution of acrylonitrile in water containing a trace of H 80 for conductivity and pH adjustment to 4, was circulated through the cell. After 4 hours no acrylamide could be detected. A trace of cyanohydrin was the only product observed.

The experiment was repeated using a 7% solution of acrylonitrile in water containing a small amount of sodium chloride for conductivity and having a pH of 6.5. After 4 hours only a trace of acrylamide was found.

In the next experiment the charge to the cell was a 7% acrylonitrile solution in water adjusted to a pH of 10.5 with sodium carbonate. After 2 hours a 20% convesion of acrylonitrile to acrylamide was found. How ever, after an additional 4 hours a sample showed no acrylamide. The pH of the solution was now down to 4.2. Apparently the amide formed was converted because of the low pH to a product that was not detected by the detection method used (vapor phase chromatography) Another run was made in which the charge was 200 parts water, buffered to a pH of 10.2 with a standard buffer solution of sodium bicarbonate and sodium hydroxide and 14 parts acrylonitrile. After 16 hours a 37% conversion of acrylonitrile to acrylamide was obtained. In this instance the final pH was 7.7. The standard buffer solution was prepared by mixing 50 mls. of 0.05 N NaHCO and 13.8 mls. of 0.1 N NaOH and diluting with water to 100 mls.

From the foregoing experiments it will be seen that a successful run was finally made when the pH was not allowed to drop below 7.

Example II Using the same conditions as employed in the successful run of Example I the process was carried out with a similar type of cell except that the cell body was made of copper instead of stainless steel.

Attempts to use a cell in which the cell body was constructed of mild steel gave low yields apparently due to the fact that iron was leeched from the cell body forming a precipitate in the product.

While the invention has been described specifically with respect to the conversion of acrylonitrile to acrylamide it is applicable to the conversion of any organic nitrile to the corresponding amide, with aliphatic and aromatic hydrocarbon nitriles containing up to about 20 or more carbon atoms being preferred. For the purpose of the invention, aromatic nitriles are defined as those nitriles having cyano groups attached to the aromatic nucleus. Representative examples of suitable nitriles include: saturated aliphatic hydrocarbon nitriles such as acetonitrile, propionitrile, pentanonitrile, dodecanonitrile, succinonitrile, adiponitrile and the like; unsaturated aliphatic hydrocarbon nitriles such as acrylonitrile, methacrylonitrile, crotonic nitrile, p-phenylacrylonitrile, Z-cyano-Z-butene, l-cyano-l-octene, 10indecenonitrile, maleonitrile, fumaronitrile, and the like; and aromatic nitriles such as benzonitrile, p-toluonitrile, a-naphthonitrile, phthalonitrile and the like. of the nitriles suitable for use in the invention, the olefinic nitriles of 3 to 6 carbon atoms are especially preferred, with the conversion of acrylonitrile to acrylamide being of special interest.

The invention is hereby claimed as follows:

1. In a process for converting a nitrile to the corresponding amide, the improvement comprising: subjecting an electrolyte containing said nitrile and water in an electrolytic cell containing spaced electrodes wherein at least one of said electrodes is made from or contains copper to a direct current between said electrodes while maintaining a pH of at least 7. V t

2. The process of claim 1 wherein one of said electrodes is stainless steel and the other is copper.

3. The process of claim 1 wherein both said electrodes are made of from or contain copper.

4. The process of claim 1 in which said nitrile is acrylonitrile and said amide is acrylamide.

5. The process of claim 1 in which the pH is within the range of 7 to about 10.5.

6. The process of claim 1 in which said electrolyte is recirculated through said cell.

References Cited UNITED STATES PATENTS 3,193,478 3,381,034 4/1968 Greene et al. 260557 R 3,616,320 10/1971 Beck et al. 204--73. A

US. Cl. X.R.

204-73 R, 73 A; 260557 R, 561 N 7/1965 Baizer 204--73 A- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 ,vs4 '494 Dated October 9 1973 Inventor(s) Ronald J. Allain and David G. Braithwaite It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4, line 26; cancel "of".

Signed and sealed this 9th day of July 1974.

(SEAL) Attest I MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents FORM PO-105O (1Q-69) USCOMM-DC 60376-P69 U.S. GOVERNMENT PRINTING OFFICE 1909 0-366-33A, 

